SEOUL (Reuters) -OpenAI will set up its first office in Seoul and has established an entity in South Korea as demand in the country jumps for its ChatGPT service, the company said on Monday. South Korea has the largest number of paying ChatGPT subscribers after the United States, according to OpenAI. "Korea's full-stack AI ecosystem makes it one of the most promising markets in the world for meaningful AI impact, from silicon to software, and students to seniors," Chief Strategy Officer Jason Kwon said in a statement.